Senior Project - DDSR

Deleted Data Space Release

StorageTek provides information storage solutions in the areas of
high-performance tape drives, automated tape libraries, disk subsystems,
networking products, integrated software and consulting. They have developed a
prototype storage device capable of storing up to four terabytes of data on a
single unit. This device is able to connect to a workstation under a number of
different operating systems, including Microsoft Windows NT 5.0 and a variety
of flavors of UNIX. The storage device consists of an array of disk drives
integrated into a single unit, along with a controller. The controller,
responsible for managing read/write operations and other tasks associated with
a typical hard drive, is also responsible for allowing the user to view
multiple drives in the array as a single drive.

The goal of the project was to provide for what is called deleted data space
release (DDSR), a function which assists a disk array subsystem in managing its
free space. Since most operating systems, including Windows NT, manage free
disk space internally, they do not usually notify a disk subsystem when space
has been freed. They only need to manipulate the disk when data is actually
being written. However, due to the nature of the disk array, it is necessary
that the disk subsystem know both when space is allocated and when it is
deallocated on the device. This project, implemented in C as a Windows NT
"filter driver," provides this mechanism.